1. Blastocyst formation: After fertilization, the zygote undergoes several cell divisions to form a ball of cells known as a blastocyst. This usually occurs within 4-5 days after fertilization.
2. Hatching of blastocyst: The blastocyst then hatches from its protective zona pellucida, which allows it to interact with the uterine lining.
3. Apposition: The blastocyst now moves towards the uterine lining and comes in close proximity to it. This process is known as apposition.
4. Adhesion: The blastocyst adheres to the uterine lining, specifically to the epithelial cells of the endometrium. The trophoblast cells, which are part of the blastocyst, play a crucial role in this adhesion process.
5. Invasion and implantation: The trophoblast cells then invade into the endometrium, which involves the breakdown and remodeling of the uterine blood vessels. This invasion allows for proper attachment of the blastocyst to the uterine lining.
6. Decidualization: The invaded endometrium undergoes a process called decidualization, where the endometrial cells undergo changes to form the decidua. The decidua provides a supportive environment for the developing embryo.
7. Establishment of placenta: The trophoblast cells continue to proliferate and differentiate to form the placenta, which is the vital organ that connects the mother to the developing embryo and provides nutrients and oxygen to the embryo.
8. Development of embryonic structures: Once implanted, the blastocyst develops further into an embryo with various embryonic structures such as the amniotic sac, placenta, umbilical cord, and fetal membranes.
Overall, the process of implantation is complex and involves various interactions between the blastocyst and the uterine lining to establish a successful pregnancy.
The physiology of implantation involves several steps:
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